At the same time, the use ofan RF accelerator as an injector is not necessarily a superior option compared to self-injection of electrons from plasma. The quality of accelerated beam in the considered pre-conceptual design is comparable to the quality of beams achieved in self-injection experiments [1]}, [2]}, [3]}, [4]}, [5]}, [6]}. The main reason for the RF accelerators failing to outperform plasma-based self-injectors is due to already mentioned difficulty to generate ultra-high peak current electron bunches, which are routinely generated from plasmas. The RF injectors have to generate longer bunches in order to produce the same overall bunch charge. That translates into the increased rms energy spread acquired by the bunch during successive acceleration in a highly nonuniform plasma wakefield.
